Hammer tip and clamp



A ril 23, 1968 Filed June 24, 1965 Ems. 3

A. F. COMPAGNONI HAMMER TIP AND CLAMP 4 Sheets-Sheet l Invenfo r zfl'nthong, F. Compagnont 55/ wallm,K-uam, nut/ D0144,

fH'torne i 's April 23, 1968 A. F. COMPAGNO NI 3,379,384

HAMMER TIP AND CLAMP 4 Sheets-Sheet 2 F. .wma w m V0 mc m 0 g E April 23, 1968' A. F. COMPAGNONI 3,379,384

HAMMER TIP AND CLAMP Filed June 24, 1965 4 Sheets-Sheet 3 mm; Mm

Inventor Anthea F. Com pagnoni. 55 Home? A F. COMPAGNONI HAMMER TIP AND CLAMP 4 Sheets-Sheet 4 April 23, 1968 ii; I 2 i i 1 Inventor Ana-w ng, F. Compagnoni inn. mun I 135 1:4 B5 f QWMQDM fi-Hzqrnegfi 2 United States Patent M 3,379,384 HAMMER TIP AND CLAMP Anthony F. Compagnoni, Chicago Heights, 11]., assignor to Aherr Corporation, a corporation of Delaware Continuation-impart of application Ser. No. 413,488, Nov. 24, 1964. This application June 24, 1965, Ser. No. 466,742

Claims. (Cl. 241-197) ABSTRACT OF THE DESCLOSURE A hammer for a hammer mill is constructed to include a shank and a detachable head having portions complemental to an insert which aids in holding the parts together.

This application is a continuation-in-part application of copending United States application Ser. No. 413,488, filed Nov. 24, 1964, and entitled, Hammer Tip and Clamp and now abandoned. This invention relates to rotary hammers and hammer heads of the type generally employed in rock crushers, reducers or hammer mills.

The present invention is directed to centrifugal hammers and hammer heads employed for comminuting rocks, ore, cement or the like. A typical installation for such hammers is a hammer mill having a easing into which are charged the rocks, ore or cement for crushing between hammer heads and breaker bars conveniently spaced about the inner periphery of the casing. Such hammers are subjected to tremendous forces and extreme conditions of shock, wear and vibration. The tips or heads of the hammers experience considerable wear due to abrasion along the outer surfaces of the hammer heads and wear more quickly at the leading edges of the head. After a considerable amount of wear on the leading edge and leading side of the hammer heads, the hammer heads are reversed to have the opposite edge placed in a leading position so as to obtain greater life or service from the hammer heads. Preferably, the hammer heads are detachable from their shanks secured to a rotor so that only the head need be replaced.

An object of the present invention is a hammer having a replaceable hammer head interlocked to a shank in a new and novel manner. Another object of the invention is to construct a hammer head and shank with a novel form of interlock which permits the hammer head to be detached without unfastening the shank from its rotary support. More specifically, under this object of the invention, the hammer has a shank portion with a flared end for insertion within a socket in the hammer head and an insert is inserted into the cavity to interlock the hammer shank to the hammer head.

Because of the tremendous forces involved and the considerable pounding and wear to which a hammer of the kind herein involved may be subjected, a further object of the invention is to so construct a replaceable hammer head and a shank as to afford large bearing surfaces over which to distribute the load between the shank and the head. More specifically, under this object of the invention, the end of the shank has a relatively long and wide surface for continuous engagement with a bottom wall of the cavity in the hammer head so that the forces are applied over these large and relatively wide bearing surfaces.

Another object of the invention is affording large hearing surfaces on the hammer shank and hammer head by curving the respective bearing surfaces.

A further object of the invention is to increase the strength of the hammer head by affording a bearing sur- 3,379,384 Patented Apr. 23, 1968 face on the hammer which surface is generally concentric with the bottom outer surface of the hammer head thereby affording a uniform wall thickness therebetween.

Another object of the invention is affording a novel h'ammer head having a longer life and more wear metal.

Another object of the invention is to construct a hammer with a one-piece shank presenting a generally T-shaped end portion insertable into a corresponding cavity in a hammer head only by rotating the hammer head relative to the T-sh'aped portion to dispose, one at a time, the arms or hooks of the T-shaped portion under shoulders formed within the socket or cavity, and having curved inserts positionable under the shoulders and against the arms of the T-shaped shank to take up the space therebetween, thereby holding the hammer head rigidly interlocked to the shank.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by Way of illustration, shows preferred embodiments of the present invention and the principles thereof and which is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a sectional view showing a hammer head being rotated on a shank;

FIG. 2 is a sectional view showing the positioning of inserts between a portion of the hammer head and shank prior to securing by an attaching nut and bolt;

FIG. 3 is a sectional view showing the attaching bolt and holding the inserts in position;

FJG. 4 is a side view of a hammer head;

FIG. 5 is a view taken along the line 55 in the direction of the arrows of FIG. 4 showing the hammer head;

FIG. 6 is a sectional view taken along the line 66 of FIG. 7 showing an insert;

'FIG. 7 is a front view of an insert;

FIG. 8 is the sectional view taken at the line 8-8 of FIG. 7 showing the cross-section of an insert;

FIG. 9 is a sectional view of another embodiment of the invention employing a single insert;

FIG. 10 is a sectional view showing the shank of FIG.

FIG. 11 is a side view of the shank of FIG. 2;

FIG. 12 is a partial sectional view of a hammer head and shank constructed in accordance with another embodiment of the invention;

FIG. 12A is a partial sectional view similar to FJG. 12 of a hammer head of smaller size; and

FIG. 13 is an elevational view of a hammer shank employed with the hammer heads of FIGS. 12 and 12A.

Referring now to the drawings and more particularly to FIGS. 1, 2 and 3, there is illustrated a hammer 15 having a shank 16 with a hammer head or tip 18 secured to the outward end of the hammer shank 16. The shank 16 and head 18 are rigidly locked together by retainer inserts 32. The hammer 15 to which the present invention is particularly adapted is employed in crushers, reducers or hammer mills wherein cement, rocks, ore or the like are comminuted by being impinged by a plurality of rotatable hammers 15 and hammer heads 18. The hammers 15 are secured to a rotor (not shown) having a plurality of spaced shafts 22 about its periphery and to which are secured the hammers 15.

In a typical installation, the rotor rotates the hammer 15 within the interior of a casing (not shown) having its walls lined with breaker bars which have a relatively hard surface for breaking and pulverizing the charge impinged thereagainst by the whirling hammers 15. In these installations, the hammers move relatively close to some of the breaker bars to grind the charge against the breaker bars as well as to drive the charge against the breaker bars. Preferably, the hammer shank 16 and the hammer head tip 18 are made from a tough, shock resistant, and wear resistant material such as manganese steel.

Even though the hammer heads 18 are made of a wear resistant material, the continuous abrasion and grinding of the charge causes the hammer heads 18 to wear along a leading edge or corner such as 24, FIG. 4, towards the opposite and upper corner 25. The leading edge is that edge leading in the direction of rotation of the hammer head 18. The life of a hammer head, such as 18, is considerably lengthened by making the hammer head reversible so that the hammer head can be reversed through 180 to have a trailing edge such as 27 moved to the forward or leading position to take the greatest wear and become the leading edge.

An important aspect of the present invention is the ability to reverse the hammer head 18 on its shank 16 without detaching the shank 16 from its rotor or support shaft 22. Many of the prior art hammers require the time-consuming detachment of a hammer shank from the rotor in order to replace or to turn a hammer head. The present invention affords a novel interlocking construction between the shank 16 and hammer head 18. This interconnection includes the lower end 30 of the shank 16, a socket or cavity 31 in the head, and one or more retainer inserts 32. More specifically, the outward or lower portion 38 of the shank 16 is fish-tailed or T- shaped to be received in the socket 31 and beneath the shoulder portions 33 on the hammer head 18, between which portions are disposed one or more inserts 32.

When attaching a hammer head 18 to the shank 16, the hammer head 18 is canted at an angle relative tothe longitudinal or lengthwise portion of the shank 16, FIG. 1, so that a first flared arm or hook 35 on the outward portion 30 of the shank 16 can be inserted through an opening 38 formed in the upper or outward surface 40 of the hammer head 18. As readily apparent from FIG. 1, the hook 35 is moved through the opening 38 into the cavity 31 formed in the hammer head so that an op posite flared arm or book portion 42 on the shank 16 may clear the surface 34 of the shoulder 33 adjacent thereto.

The length of the outward portion 30 of the shank 16 between the hooks 35 and 42 is of a greater dimension than the opening 38 between the side walls 44 and 45, .FIG. 5. Thus, the outward portion 30 of the shank 16 cannot be inserted within the recess or opening 38 without cocking the hammer head relative to the shank 16 and inserting one of the hooks 35 or 42 into the opening and below its curved shoulder 34 prior to rotating the hammer head 18 relative to the other hook. With the hooks 35 and 42 moved into the cavity 31, the outermost end and bearing surface 47 is brought into juxtaposition relative to the bottom surface and bearing surface 48 in the opening of the hammer head 18. The bearing surfaces 47 and 48 are disposed opposite one another and extend for a considerable area to afford large flat bearing surfaces behind the impact area of the tip over which to distribute impact forces.

To hold the bearing surfaces 47 and 48 tightly against one another and to prevent relative movement between the hammer head 18 and the shank 16, a pair of retainer inserts 32 are adapted to be slid into position between the curved shoulder surface 34 of the hammer head and a concavely curved surface 50 formed between the hooks 35 and 42 and the body portion 52 of the shank 16.

The inserts 32 have a concave, curved surface 54 for complementary engagement with the convex, curved sur- .4 faces 34 of the shoulders 33 and have a convexly curved surface 55 adapted for snug and complementary engagement with a concavely curved surface 50 on the shanks 16. Preferably, the lower portion of the retainer inserts 32 is bifurcated to provide a pair of lugs or toes 56 and 57, FIG. 7, which are adapted to be disposed in complementary shaped openings 58 and 59, FIG. 4, in

side walls 68 and 69 of the hammer head 18. As best seen in FIG. 6, the toes 56 and 57 of the inserts 32 are disposed to extend outwardly from the plane of an upper or main body portion 62 of the retainer 32. Also, the insert 32 has a lug portion 60,FIG. 6, depending downwardly between the toes 56 and 57. The inward surface 61 of the dependent lug 60, FIG. 6, has the same convex curvature as the surface 55 of the toes 56 and 57 for engagement with the concave complementary surfaces 50 on the shank 16, as best seen in FIG. 3.

Each of the retainer inserts 32 is formed with a cavity seat 63 for receiving either the head of a bolt 64 or a nut 65 which are adapted to be tightened to secure the inserts 32 to the shank 16, as best seen in FIG. 3. The seat 63 is centrally aligned with an opening 66 through which the shank of the bolt 64. may be inserted. When the bolt 64 and nut 65 are locking the inserts 32 on the shank 16, as illustrated in FIG. 3, the inserts 32 have the ends of their toe portions 56 and 57 aligned with the surface of the side walls 68 and 69. The inserts 32 have a rectangular boss 71, with a lower shoulder 70 for seating on a complementary shaped seat 72, FIG. 3, formed in the hammer shank 16.

Preferably, a bridging member or portion is disposed between the openings 58 and 59, FIG. 4, for the bifurcated toes 56 and 57 so as to afford additional strength to the side walls 68 and 69 of the hammer head.

In the preferred form of the hammer head 18, as illustrated herein, the hammer head 18 is generally block shaped with four side walls 68, 69, 73 and 74 with an upper or top wall 40. The lower or bottom wall between the edges 24 and 27 is convexly curved. The cavity or recess 31 is generally cubic in shape in that it is defined by planes parallel to the side walls 43, 44 and 45 and top wall 40 and bottom wall 48.

Thus defined, the openings 58 and 59 extend normal of this generally cubic cavity 31 and afford additional cavities beneath the shoulders 33 of the hammer head 18.

The shank 16 fits snugly between the side walls 44 and '45 in the socket.31 and prevents relative shifting between the shank.16 and the hammer head 18 in the direction of the arrow A, FIG. 5. The bifurcated toes 56 and 57 also serve to prevent relative movement between the shank 16 and the hammer head 18 when inserted in the openings 58 and 59 so as to be in contact with the opposite walls 78 and 79 of the. respective openings 58 and 59.

As best seen in FIG. 11, the flared hook portions 35 and 42 are bifurcated at the center thereof to afford a slot 36 adapted to receive the bridging portion 75. This slot 36 facilitates the rotation of the hammer head 18 on the shank 16 by allowing the hook portions 35 and 42 to be disposed more closely toward the outer side wall 68 and 69 while the other hook portion is being moved through the opening 38. If the slot 36 were not provided, then the flare of the hook portions 35 and 42 would have to be substantially reduced due to engagement of the hook portions 35 and 42 with the interior surface 76, FIG. 3, of the bridge member 75.

To prevent relative movement between the hank 16 and the hammer head 18 in direction of the arrow B, FIG. 5, the retainer inserts 32 .fit snugly between the shoulder surface 34 of the hammer head 18 and the curved surface 50 of the shank 16. The retainer inserts 32 also fit snugly between the lower surfaces of the shoulders 33 and curved surfaces 50 onthe shank 16 to hold the bearing surfaces 47 and 48 in relatively tight engagement. Thus, with the shoulders 70 of the inserts 32 disposed in the receiving seats 72 on the shank 16 and with bolt 64 through the openings in the inserts 3'2 and shank 16, the hammer head 18 is rigidly secured to the shank 16 without relative movement therebetween.

The geometrical configuration of the hammer shank 16 and hammer head 18 thus provided considerable area over which to distribute the impact forces, the major areas are as follows (1) the large impact bearing 47 on the shank and mating fiat surface 43 on the hammer head 18, (2) the mating impact areas on the head walls 44 and 45 and respective oppositely disposed areas of the shank 16 and (3) overhanging surfaces 60 A, FIG. 11, which are adapted to fit flush against the top surface 40 of the hammer head 18. This is in contrast to the prior art hammers and shanks wherein the shank was more in the nature of a hook on which the hammer head was hung without the advantage of the large amount of impact area afforded by the present invention.

While the preferred embodiment of the invention illustrated in FIGS. 1 to 8, inclusive, has two inserts 32, it is also within the purview of the present invention to employ only a single insert, hereinafter designated by the reference character 80, FIG. 9, of the same general configuration as the insert 32 hereinbefore described. As most readily apparent, the retainer insert 80 is employed with a shank 16A having its lower flared or hook portion 32 thickened, that is, enlarged in cross-sectional area at the surface 83 for direct engagement with a convex surface 3-4, on a shoulder 33. The outer portion 82 of the shank 16A has toes, similar to toes S6 and 57, adapted to be inserted into the openings 58 and 59 on one side of the hammer head 18. The opposite hook portion 35 has been partially cut away along an oblique line 79 so as to avoid interference with the shoulder surface 34 When the hammer head 18 is rotated on the shank 16A. It is necessary to reduce the length of the hook portion 42A because of the increased thickness of the shank 16A.

The opposite shoulder 34 engages a com-plemental and concavely curved surface 33 on the insert 86 and a convex surface 34, and the retainer 89 engages the complementary curved surface 85 on the shank 16A. A smaller bolt 85 is disposed with its head within a seat formed in the insert St and a nut 87 is threaded on a bolt 85 seated within an opening 88 formed in the shank 16A. Thus, the bolt 85 and nut 87 are adapted to hold the insert 8t) against outward movement or loss while the hammer head is rotating. Thus, it should be readily apparent that the single insert 80 functions in the same general manner as the inserts 32 to fit snugly between the surface 85 on the shank A and the surface 34 and the head 18 to prevent any sliding or relative movement between the hammer head 18 and shank 16A.

As best seen in FIG. 10, the shank 16 A has an upward or collar portion 96 through which extends a longitudinal bore d1 for being received on the shaft 22 on the rotor or the hammer mill. The hammers are suitably keyed or are oth rwise affixed to the shaft 22 or other portion of the rotor to secure the hammer for rotation in the mill.

While the inserts 32 and 89 are described as having two toes 56 and 57, it is to be understood that these inserts may be constructed with only a single Wide toe or with more than two toes. When only one toe is employed, the bridging member 75 is removed to leave a single large opening in the side walls 6 8 and 6 9 to receive the toes. When an insert having only a single wide toe is employed, it is preferred that the shank 16 have its flared or hook portions 35 and 32 not bifurcated by the slot 36, FIG. 11.

Also, it is to be understood that the portion of the cavity 31 underlying the shoulders 33 need not extend through the side walls 68 and 69', that is, to form the penings 58 and S9 in the side walls 68 and 69. The walls 68 and 69 are preferably perforated by the openings 5S and 59 so that the cavity 31 can be easily cleaned by running a tool through openings 58 and 59 to dislodge any accumulations of material in the cavity 31.

A further embodiment of the invention is shown in FIGS. 12, 12A and 13, wherein the centrifugal hammer 15 is constructed of generally the same elements; but employs a rounded or curved configuration at the end of the shank and at th bottom of the cavity in the hammer head. In the embodiment of the invention illustrated in FIGS. 12, 12A and 13, the reference characters designating portions on the hammer shank, insert'means and hammer head are similar to those employed hereinbefore except that ther has been added the numeral 1 (one) in the hundreds column of the character designation to afford a one hundred plus designation. For instance, the shank is designated by the reference character 116 and the hammer head is designated by the referenc character 118.

An important aspect of the embodiment of the invention hereinafter described in conjunction with FIGS. 12, 12A and 13, is that the bearing surface 147 on the shank 116 and the bearing surface 148 in the hammer head 118 are curved in a generally concentric relationship to the curvature of the bottom wall 110, FIG. 12, of the hammer head 113. An advantage realized by the curvature of bearing surfaces 147 and 148 is that of affording a larger bearing surface or area than is afforded with the noncurved area for the bearing surfaces 47 and 48 of the hereinbefore described embodiments of the invention. Thus, with the curved surfaces 147 and 148, additional surface area is provided between the shank'116 and hammer head 118 over which to distribute the impact forces of the hammer head 118.

Another significant advantage in the affording of the curved surfaces 147 and 148, as distinguished from the aforementioned flat surfaces 47 and 48, which are indicated in phantom line of FIG. 12, is that of a more uniform, cross-sectional, thickness of metal in the hammer head 118 between the bottom surface 148 of the recess 131 and the curved, outer wall 116 of the hammer head 118. This uniform wall thickness provides additional strength thereby affording a longer life for the hammer head. Also it should be noted that the curved bearing surface 148 encounters the side walls 144 and 145 in generally rounded corners 111 and 112 which are disposed upwardly above similar corners 111A and 112A which would be formed by affording a fiat planar surface such as 47 above described.

It will be appreciated that additional wall thickness is thereby provided between the corners 111A and 112A and the respective leading edges 124 and 127 than is afforded with a fiat bearing surface 47. Moreover, as the hammer head 118 wears from one of the leading corners 124 or 127 generally towards its respectively, associated corners 111 or 112 in the bottom of the shank cavity 31 of the hammer head 118, more useable metal is afforded at leading corners 124 and 127 by the curved surface 148 thereby lengthening the period before the wall thickness is reduced to a minimum limit. Thus, longer life and more useable metal is afforded for the hammer head 118 having the aforementioned construction.

While not described in detail, it is to be understood that at least one insert 132, and preferably two inserts 132 are provided in the manner hereinbefore described with reference to FlGS. 1-3, for securing the hammer head 118 and hammer shank 116 in assembled relationship With the bearing surfaces 147 and 148 in a juxtaposed position in face to face relationship. FIG. 12A illustrates generally the same configuration of hammer head except that the cross-sectional thickness of the metal between the surfaces'148 and is reduced in thickness from that of FIG. 12.

From the foregoing, it will be seen that the present invention affords a unique hammer or hammer assembly having a shank interfitted and interlocked to a hammer head. A worn or broken hammer head can be replaced or turned about without removing the shank from its support on the rotor. Also from the foregoing, it will be seen that novel inserts rigidly hold the hammer head on the shank. Also, the hammer head can be readily reversed or replaced without removing the shank from its shaft support.

Also, the hammer affords large bearing surfaces between the hammer shank and hammer head over which to distribute the impact forces. By making these bearing surfaces curved and complementary fitting with each other, increased bearing surface may be provided. When the bearing surface on the bottom of the shank-receiving recess is generally concentric with the bottom wall of the hammer head, a uniform cross-sectional thickness of metal is provided thereby affording increased strength. Also, a curved surface at the bottom of the shank-receiving opening may afford longer life and more wear metal.

Hence, while I have illustrated and described preferred embodiments of my invention, it is to be understood that these are capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. A centrifugal hammer having a single shank member having one end portion for attachment to a rotary mill member, a second end portion on said shank having arms extending normally of said shank to constitute a generally T-shaped end portion, a hammer head having a central recess to receive said second end portion and having an opposite work portion positioned away from said shank, said central recess having internal cavities extending to make said central recess of a greater dimension than said second end portion, said recess forming overhanging walls within said hammer head, insert means positioned in said opening and against said shank and under said overhanging walls, said insert means extending into said internal cavities, and means for securing the insert means in place.

2. In a centrifugal hammer having a single shank member for attachment to a rotor of a mill and having a replaceable hammer head secured to said shank, an end portion on said shank having arms extending normal of said shank to constitute a generally T-shaped end portion, an access opening in the top of said hammer head for receiving said end portion of said shank, said access opening leading to cavities extending normal toward opposed side walls of said hammer head, said access opening being of a lesser dimension than the dimension of said arms of said end portion so that a first of said arms must be inserted into one of said cavities and said hammer head rotated relative to said shank to insert the other of said arms through said access opening, and insert means inset-table through said access opening into said cavities to take up space between said arms and said hammer head in said cavities and between said shank and said hammer head and said access opening, said insert means having a portion extending above said access opening, and fastener means for fastening said portion of said insert means extending above said access opening to said shank.

3. A centrifugal hammer for attachment to a rotor of a hammer mill or the like comprising: a shank means for connection to said rotor, a hammer head detachably mounted on said shank means and reversible in its connection with said shank means, a generally rectangular shaped recess in a surface of said hammer head for receiving the end portion of said shank means remote from the portion of said shank means attachable to said rotor, said end portion of said shank means having a generally rectangular portion for being disposed in said recess of said hammer head and of the same general dimension in one direction and of a lesser dimension in the other direction compared to said recess, said recess leading to openings in said opposite side walls of said hammer head,

said end portion being flared at the end thereof and adapted to be seated in said normal side wall openings when said end portion is disposed in said recess, insert means insertable into said recess and having a portion insex-table into said side wall openings to take up space between said flared portion of said shank means and said hammer head, said insert means filling the space between said shank means and said hammer head in said recess, a portion of said insert means extending along said shank means and outwardly of said hammer head, and fastener means for securing said outward portion of said insert means to said shank means to hold said insert means in its interlocking position between said hammer head and said shank means.

4-. In a centrifugal hammer having a single shank member for attachment to a rotor of a mill and having a replaceable hammer head secured to said shank, an end portion on said shank having arms extending normal of said shank, said hammer head having a top wall, bottom wall, and opposed side walls, a cavity extending interiorly of said hammer head from said top wall for receiving said end portion of said shank, openings in a pair of opposed side walls extending into said cavity, said arms of said shank end extending toward said openings in said side walls, insert means having a portion positionable against the shank at said cavity to substantially fill said cavity at said top wall, arcuate toe means on said inert means insertable into said cavity and openings in said side walls to substantially till the space in said cavity above said arms, and fastener means for fastening said insert means to said shank.

5. The hammer of claim 4 wherein said openings extending into said cavity define shoulders thereabove, said shoulders having convexly, curved surfaces, and wherein said inserts have concavely, curved surfaces for engagement with said convexly curved surfaces.

6. The hammer of claim 5 wherein said toe means includes a pair of bifurcated toes.

7. In a hammer mill or the like, the combination comprising: a rotatable member, a hammer secured to said member, a shank on said hammer connected to said member, a hammer head detachably mounted on said shank and reversible in its connection with said shank without necessitating removal of said shank from said member, an opening in a surface of said hammer head for receiving the end portion of said shank remote from the portion of said shank attachable to said member, said end portion of said shank having a portion for being disposed in said opening of said hammer head and of the same general dimension as the opening in one direction to prevent relative movement between said hammer head and said shank in said one direction, said shank end portion being flared at the end thereof and adpated to be seated in said opening, insert means insertable into said opening and having a portion to take up space between said flared portion of said shank and said hammer head, a portion of said insert means extending along said shank and outwardly of said hammer head, and fastener means for securing said outward portion of said insert means to said shank to hold said insert means in its interlocking position between said hammer head and said shank.

8. An insert for securing a hammer head having a cavity with an overhanging shoulder to a hammer shank having a flared end with concave surfaces thereon, said insert comprising: a body member having an insert portion adapted to be inserted into a space between said cavity and said head, said insert portion having an arcuate and concave surface adapted for mating engagement with said overhanging shoulder, said insert portion having a,

convexly curved surface for mating engagement with said concave surfaces of said shank, a fastener portion extending at an angle to said insert portion, and said fastener portion adapted to move along said shank and having an aperture therein for receiving a fastener to lock said insert to said shank.

9. In a centrifugal hammer, shank means, a hammer head replaceably mounted on said shank means, said shank means having a terminal portion and a leg presenting a curved surface, said hammer head having an opening therein for receiving said terminal portion and leg of said shank means, curved Wall means within said hammer head opening and presenting a surface having a curvature complementary to said curved surface on said shank means, said complementary curved surfaces being spaced one from another, insert means insertable into said opening between said complementary curved surfaces for interlocking said shank means with said hammer head with the respective curved surfaces and means for holding said insert means in place between said complementary curved surfaces.

Iii). in a centrifugal hammer, shank means terminating in an end portion presenting a leg having a curved hearing surface, a replaceable hammer head mounted on said shank means, said hammer head having a shank receiving opening therein, said hammer head having outer side walls, an upper, outer wall, and an opposed, lower outer Wall, said opposed lower Wall being curved netween at least two of said side Walls, a curved bearing surface within said receiving opening of a curvature complementary to the curvature of said bearing surface on said shank means, separate insert means positioned between said complementary bearing surfaces, and means to secure the insert means in place.

References Cited UNITED STATES PATENTS 2,994,486 8/1961 Trudeau 241l97 2,379,752 7/1945 Schultz 287-20.5 2,568,077 9/1951 Loufek 241-197 3,272,445 9/1966 Weller 241l97 ANDREW R. JUHASZ, Primary Examiner. 

